Gearless spring washer high torque device

ABSTRACT

Disposable torque-limiting mechanisms with upper shank component with a torque-limiting interface, a lower shank component with a torque-limiting interface, and a washer assembly biasing element. Torque-limiting interfaces having a plurality of undulations arranged around an axial bore or drive socket and separated by a plurality of transition regions, with each undulation having an upslope, a peak, and a downslope. The torque-limiting interfaces are configured to engage and disengage to provide torque transmission with predetermined torque limits at various rotational speeds and for amounts of actuations while remaining within a specified operational range.

CROSS-REFERENCE

This application is a Continuation patent application of U.S. patentapplication Ser. No. 15/583,803 filed May 1, 2017, which claims priorityto International Patent Application PCT/US2016/055798, filed Oct. 6,2016, which claims priority to U.S. Provisional Patent Application Nos.62/238,419, filed Oct. 7, 2015, U.S. Provisional Patent Application62/238,359, filed Oct. 7, 2015, U.S. Provisional Patent Application62/345,607, filed Jun. 3, 2016, and International Patent ApplicationPCT/US2016/035712, filed Jun. 3, 2016, the contents of which isincorporated here in their entirety.

BACKGROUND 1. Field

This disclosure relates to gearless torque drives for torque-limitingdevices that are suitable for operation at high rotational speeds.

2. General Background

Torque is a measure of force acting on an object that causes that objectto rotate. In the case of a driver and a fastener, this measurement canbe calculated mathematically in terms of the cross product of specificvectors:

τ=r×F

Where r is the vector representing the distance and direction from anaxis of a fastener to a point where the force is applied and F is theforce vector acting on the driver.

Torque has dimensions of force times distance and the SI unit of torqueis the Newton meter (N-m). The joule, which is the SI unit for energy orwork, is also defined as an N−m, but this unit is not used for torque.Since energy can be thought of as the result of force times distance,energy is always a scalar whereas torque is force cross-distance and sois a vector-valued quantity. Other non-SI units of torque includepound-force-feet, foot-pounds-force, ounce-force-inches,meter-kilograms-force, inch-ounces or inch-pounds.

Torque-limiting drivers are widely used throughout the medical industry.These torque-limiting drivers have a factory pre-set torque to ensurethe accuracy and toughness required to meet a demanding surgicalenvironment.

The medical industry has made use of both reusable and disposabletorque-limiting drivers. In a surgical context, there is little room forerror and these drivers must impart a precise amount of torque.

Reusable drivers require constant recalibration to ensure that thedriver is imparting the precise amount of torque. Recalibration is acumbersome task but must be done routinely. Such reusable devices alsorequire sterilization.

Disposable drivers are an alternative to the reusable drivers. Once thedriver has been used, it is discarded.

Disposable drivers are traditionally used for low torque applications.The standard torque values in these applications typically range fromabout 4 to about 20 inch-ounces. It has, however, been a challenge todevelop a reliable disposable driver capable of imparting higher torquesfor larger applications.

Power tools are used for some applications in the medical industry. Suchpower tools can provide torque to a workpiece while also providinghigher rotational rates than can be provided with manually driven tools.Torque-limiting systems can be utilized with medical power tools, eitheras an additional attachment provided in-line between the power tool andthe workpiece or as internalized systems within the power tool itself.Reusable torque-limiting systems need to be sterilized between uses andtypically must be serviced and recalibrated periodically to ensureperformance within specifications. Disposable torque-limiting systemsare an alternative to the reusable systems. Once the torque-limitingsystem has been used, it is discarded.

Disposable torque-limiting devices which are inexpensive for use withpower tools can fall out of specification with increased RPMs and assuch fail to perform sufficiently.

Thus there is a need for disposable torque-limiting systems that can beutilized with medical power tools to limit applied torque at higherrotational speeds and remain in specification over a predeterminednumber of actuations. The disclosure is directed to these and otherimportant needs.

DISCLOSURE

Aspects of exemplars of torque-limiting devices, methods and mechanismsare disclosed herein, in some exemplars a generally hollow cylindricalbody with a partially closed distal end provides an upper shank formedinside the partially closed distal end of the cylindrical body; acircumferential rim is formed on the outside of the partially closeddial end; an upper torque-limiting interface is formed on the inside ofthe partially closed distal end having an axial bore; a lower shankcomponent is placed in the body and free to rotate axially, it furthercomprises a proximal end, a distal end, a neck extending from the distalend, a drive socket fluidly connecting the proximal end and the distalend, and a lower torque-limiting interface disposed on the proximal end,wherein the upper shank component and the lower shank component arealigned along an axis in the direction of the axial bore and the drivesocket with the first torque-limiting interface in contact with thesecond torque-limiting interface; an MBWA placed above the lower shankon at least partially around the neck configured to apply compressiveforce (F) along the axis to compress the first torque-limiting interfaceagainst the second torque-limiting interface; a tool collar with aflange extending radially therefrom with a front on one side of theflange, a square leg formed on the opposite of the flange and a shapedchannel therethrough is rotatably fit into the circumferential rim; atool shaft with a threaded back portion and a front end having a toolchannel therein; catches are formed on the tool shaft configured to matewith the shaped channel whereby the tool shaft can be inserted throughthe tool collar but rotate within the shaped channel; a threadedretaining member is configured to engage the threaded back portion; andwherein the tool shaft and threaded retaining member cooperate to applya predetermined force to the lower and upper shanks, (the two interfacestogether form a torque limiting engagement), by mounted the tool shaftthrough the tool collar, the axial bore, the drive socket and the MBWAand affixing the retaining member thereto.

In some instances in the above exemplars the MBWA is configured to applycompressive force (F) along the axis to compress the firsttorque-limiting interface against the second torque-limiting interface;the upper shank component and the lower shank component are configuredto engage to rotate together when torque is applied to the lower shankcomponent via the drive socket; and, the upper shank component and thelower shank component are configured to disengage when a predeterminedtorque limit is exceeded.

In some instances the above exemplars further comprise a plastic highlubricity washer between the flange and the circumferential rim. In yetother instances the exemplars include a roller bearing washer betweenthe flange and the circumferential rim.

Disclosed is a novel disposable torque-limiting device with one or moreof a torque limiting interface, a drive assembly with reducedcomponents, a shaped washer force assembly with reduced components,simple assembly, operation for a limited predetermined number of cyclesat high speed. Cycles are a measure of the life time of the disposabledevice.

Aspects of exemplars of torque-limiting devices, methods, and mechanismsare disclosed herein, in some exemplars a generally hollow cylindricalbody with a partially closed distal end provides an upper shank formedinside the partially closed distal end of the cylindrical body; acircumferential rim is formed on the outside of the partially closeddial end; an upper torque-limiting interface is formed on the inside ofthe partially closed distal end having a axial bore; a lower shankcomponent having a proximal end, a distal end, a retaining cavity formedthereon, a drive socket fluidly connecting the proximal end and thedistal end, and a lower torque-limiting interface disposed on theproximal end, wherein the upper shank component and the lower shankcomponent are aligned along an axis in the direction of the axial boreand the drive socket with the first torque-limiting interface in contactwith the second torque-limiting interface; an MBWA placed above thelower shank on at least partially around the neck configured to applycompressive force (F) along the axis to compress the firsttorque-limiting interface against the second torque-limiting interface;a tool collar with a flange extending radially therefrom with a front onone side of the flange, a square leg formed on the opposite of theflange and a shaped channel therethrough is rotatably fit into thecircumferential rim; a tool shaft with a threaded back portion and afront end having a tool channel therein; catches are formed on the toolshaft configured to mate with the shaped channel whereby the tool shaftcan be inserted through the tool collar but rotate within the shapedchannel; a threaded retaining member is configured to engage thethreaded back portion; and wherein the tool shaft and threaded retainingmember cooperate to apply a predetermined force to the lower and uppershanks, (and the two interfaces together form a torque limitingengagement), by mounted the tool shaft through the tool collar, theaxial bore, the drive socket and the MBWA and affixing the retainingmember thereto.

In some instances in the above exemplars the MBWA is configured to applycompressive force (F) along the axis to compress the firsttorque-limiting interface against the second torque-limiting interface;the upper shank component and the lower shank component are configuredto engage to rotate together when torque is applied to the lower shankcomponent via the drive socket; and, the upper shank component and thelower shank component are configured to disengage when a predeterminedtorque limit is exceeded.

In some instances the above exemplars further comprise a plastic highlubricity washer between the flange and the circumferential rim. In yetother instances the exemplars include a roller bearing washer betweenthe flange and the circumferential rim. In some instances the aboveexemplars further comprise a tool in the tool channel.

In some instances in the above exemplars the first torque-limitinginterface has a first plurality of undulations arranged around the axialbore and separated by a first plurality of transition regions; thesecond torque-limiting interface comprises a second plurality ofundulations arranged around the drive socket and separated by a secondplurality of transition regions, the first and second pluralities beingequal in number; and each undulation comprises an upslope, a peak, and adownslope.

In some instances in the above exemplars of the torque-limiting deviceeach upslope has an inclination angle between about 3 degrees and about15 degrees.

In some instances in the above exemplars of the torque-limiting deviceeach upslope has an inclination angle between about 5 degrees and about9 degrees.

In some instances in the above exemplars of the torque-limiting deviceeach upslope has an inclination angle between about 6 degrees and about8 degrees.

In some instances in the above the predetermined torque limit is betweenabout 0.1 Newton-meters and 3.0 Newton-meters. In some instances in theabove exemplars the predetermined torque limit is between about 3.0Newton-meters and 6.0 Newton-meters.

In some instances in the above exemplars of the torque-limiting devicethe first torque-limiting interface and second torque-limiting interfaceeach comprise between two and five undulations. In some instances in theabove exemplars of the torque-limiting device the first torque-limitinginterface and second torque-limiting interface each comprise threeundulations.

In some instances in the above exemplars of the torque-limiting devicethe disposable torque limiting device is a generally hollow cylindricalbody with a partially closed distal end; an upper shank formed insidethe partially closed distal end of the cylindrical body; acircumferential rim formed on the outside of the partially closed dialend; an upper torque-limiting interface having undulations formed on theinside of the partially closed distal end having a axial bore; a lowershank component rotatable placed within the cylindrical body comprisinga proximal end, a distal end, a retaining cavity formed thereon, a drivesocket fluidly connecting the proximal end and the distal end, and alower torque-limiting interface having undulations disposed on theproximal end, wherein the upper shank component and the lower shankcomponent are aligned along an axis in the direction of the axial boreand the drive socket with the first torque-limiting interface in contactwith the second torque-limiting interface; an MBWA placed above thelower shank inside the retaining cavity configured to apply compressiveforce (F) along the axis to compress the first torque-limiting interfaceagainst the second torque-limiting interface at a predetermined torquelimit; a tool collar with a flange extending radially, a front on oneside of the flange, a square leg formed on the opposite of the flangeand a shaped channel there through rotatably fit into thecircumferential rim; a tool shaft with a threaded back portion and afront end having a tool channel therein; catches formed on the toolshaft configured to mate with the shaped channel whereby the tool shaftcan be inserted through the tool collar but rotate within the shapedchannel; and a threaded retaining member configure to engage thethreaded back portion.

In some instances each undulation is a complex shaped wave which limitsdegradation of inexpensive plastic materials and provides nominaltorque.

In some instances the first section of each undulation with a highershoulder near the center of the shank and a slope downward to theperimeter of the shank; a second section having a wide plateau; a thirdsection having a plateau wider than the second section; a fourth sectionhaving a plateau with height greater than all other section; and a fifthsection forming a sloped transition region.

In some instances in the above exemplars of the torque-limiting devicethe torque-limiting mechanism provides a predetermined torque betweenabout 0.1 Newton-meter and about 6.0 Newton-meters of torque at arotational speed between about 50 RPM and about 1300 RPM over at leastone of 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 105, 110, 120, 150,180, 200, 220, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750,800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1250, 1300, 1350,1400, 1450, 1500, 1550, 1600, 1650, 1700, 1750, 1800, 1850, 1900, 1950,2000, 2100, 2200, 2300, 2400, or 2500 actuations while remaining withina specified operational range.

DRAWINGS

The above-mentioned features of the present disclosure will become moreapparent with reference to the following description taken inconjunction with the accompanying drawings wherein like referencenumerals denote like elements. In addition, the drawings are notnecessarily drawn to scale. In the drawings:

FIG. 1A shows an exploded assembly perspective view back to front ofsome aspects of an in-line torque limiting device of the presentdisclosure.

FIG. 1B shows a cutaway front view of some aspects of an in-line torquelimiting device of the present disclosure.

FIG. 1C shows an exploded assembly perspective view front to back ofsome aspects of an in-line torque limiting device of the presentdisclosure.

FIGS. 1D and 1E show side views of biasing assembly arrangements.

FIG. 2 shows an exploded assembly perspective view back to front of someaspects of a torque limiting device of the present disclosure.

FIG. 3 shows an exploded assembly perspective view of some aspects oftorque-limiting mechanisms of the present disclosure.

FIG. 4 shows a perspective view of some aspects of the upper shank ofthe present disclosure.

FIG. 5 shows a perspective view of some aspects of components oftorque-limiting mechanisms of the present disclosure.

FIG. 6A shows a top view of some aspects of components oftorque-limiting mechanisms of the present disclosure.

FIGS. 6B-6F show cut-away sectional views along the sections marked A-A,B-B, C-C, D-D, and E-E in FIG. 4A.

FIGS. 7A and 7B show perspective views of some aspects of components oftorque-limiting mechanisms of the present disclosure. FIG. 7C shows aside view of some aspects of components of torque-limiting mechanisms ofthe present disclosure. The distal end 102 of the lower shank isvisible. The open top 105 of the annular wall forming retaining cavity103 is also visible. FIG. 7D shows a cut-away section view along thesection marked F-F in FIG. 7C.

FIGS. 8A and 8B show testing data from testing of an implementation ofthe torque-limiting mechanisms of the present disclosure.

FIG. 8C shows testing data from testing of a prior art torque-limitingmechanism.

FIG. 8D shows testing data from testing of an implementation of thetorque-limiting mechanisms of the present disclosure.

As shall be appreciated by those having ordinary skill in the art, thefigures are not to scale, and modifications to scale within a figure oracross the figures are considered within the present disclosure. Allcallouts in Figures are hereby incorporated by this reference as iffully set forth herein.

FURTHER DISCLOSURE

Aspects of torque-limiting drivers are provided in exemplaryimplementations of this disclosure. Those of ordinary skill in the artwill recognize small design variations that are within the scope of thisdisclosure. The identification of some aspects and not others shall notbe considered limiting in the disclosure but may be limitations inclaims.

FIGS. 1A-1E illustrate aspects of implementations of torque-limitingin-line drivers 10. FIGS. 2-7D illustrate additional aspects of torquelimiting drivers including operation of the torque limiter.

The driver has a generally cylindrical shape with a cup shaped drive cap12 with connector mount or other structure to facilitate use by a user.In some instances the drive cap may support or be connected to a handleor other finger fold to allow manual rotation of the device. Forexample, the drive cap is affixed to a generally hollow cylindrical body14. The cap 12 is mated to the cylindrical body at the proximal end 15of the cylindrical body. The cap 12 may be snap-fitted to cylindricalbody 14, or may be welded, adhered, or attached by any equivalentthereof.

The hollow cylindrical body 14 has an open distal end 16 with acircumferential rim 17 on the exterior therein proving a seat and guidefor a tool collar 20. A lower shank 100 is fit inside the body 14. Thelower shank is generally cylindrical of a size to allow to rotateaxially within the body. Opposite the circumferential rim on theinterior 18 of the cylindrical body 14 is an upper shank component 200formed as part of the cylindrical hollow body 14 with at least an axialbore 210 and a upper or second torque-limiting interface 250 disposed onthe inside of the cylindrical body 14.

The tool collar is formed of plastic and is a guide for a shaft. Thetool collar 20 has a flange 22 extending radially of a size and shape tofit rotatably into the circumferential rim 17. The tool collar has aroughly square leg 25 extending on one side of the flange 22 and a nose27 extending on the opposite of the flange. A shaped channel 29 passesthrough the tool collar thereby forming a fluid connection.

During assembly the lower shank component 100 fits movably within thehollow body 14. The lower shank has a drive shaft 110 therethrough. Onone side of the lower shank there is a lower or first torque-limitinginterface 150 and the other side of the lower shank 100 may include aretaining cavity 103 configured to retain biasing elements, such as agrouping of belleville washers, also known as a coned-disc spring,hereinafter referred to as Multiple Belleville Washer Assembly (“MBWA”)70 with a fluid passage 72 through the center of member. Each washermember 73 has a base 74 and a cone 75 and they are set in pairsalternating with base 74 to base 74 and cone 75 to cone 75 with a fluidpassage 72 therethrough. In other instances the washer members 73 arestacked as shown in FIG. 1E. A flat washer 36A and 36B are placed oneither end of the stack of washer members 73. In some implementations,compressible materials with durometer ratings between about 50 durometerand 100 durometer are used, within an annular wall 104. A tool shaft 31fits firmly into the tool collar channel 29. The tool shaft may bepartially hollow with an open front end 31. One or more catches 33 areformed on a portion of the tool shaft whereby the catches mate with thechannel 29 and the tool shaft 32 is restricted from rotation within thechannel 29. The catches are depicted as one or more flat sides in FIGS.1A-1C. A tool channel 34 extends axially, at least partially, in thetool shaft from the front end 31 of the tool shaft. A series of threads35 are formed on a back portion of the tool shaft 32. Optionally a firstwasher 36 is interposed between the flange and circumferential rim 17.The washer is formed of plastic and has high lubricity. In someinstances depending on design requirements and use a flat roller bearingwasher 36′ between a first washer 36C and a second washer 36D may beused with or in place of the washer 36. At higher speed the rollerbearing washer reduces frictional forces at the circumferential rim 17.Aspects of the method of in-line torque application at predeterminedforces include reducing or eliminating melting of the circumferentialrim during the life time of the device.

The lower shank 100 is inserted into the body 14 through the proximalend 15 and the lower torque-limiting interface 150 sits on the uppertorque-limiting interface 250 and the two interfaces together form atorque limiting engagement. The lower shank is generally cylindrical ofa size to allow to rotate axially within the body. The square leg andtool shaft extends through the axial bore 210 and the drive shaft 110.Formed as part of the drive shaft 110 are a series of drive catches 115which mate with the square legs 25 whereby when the lower shank 100rotates the square leg rotates as does any tools and the affixedtherein.

A threaded 37 retaining member 38 such as a nut or other fixture fitsonto the threads 35 of the tool shaft and is used to compress the MBWA70 against the lower shank and hold the components inside the deviceinline. Optionally, a washer 39 may be placed between the MBWA 70 andretaining member 38. This engagement provides a locking mechanism fortool shaft 32 relative to the body 14 via lower shank 100 when pressureis applied across lower shank 100 and upper shank 200. A preselectedforce is applied across lower shank 100 and upper shank 200 via MBWA 70within cylindrical body 14. To seal the device, at the end of the drivecap 12 is the connector mount 13 shown formed on the drive cap. Theconnector mount 13 provides a fixation of a back drive shaft 42 for apowered in-line torque limited driver (not shown).

In operation the drive shaft 40 which has a workpiece engaging tip 41 isconnected via the tip to a workpiece, fastener, or other fixture thatrequires rotation for application. The application of a rotational forceto the device causes the first torque-limiting interface 150 and thesecond torque-limiting interface 250 (collectively referred to as thetorque limiter) support on the shanks to engage and rotate the tooluntil such time as the amount of force necessary to rotate the toolfurther is exceeded by the force the tool is experiencing duringoperation. At that point the torque-limiter disengages and one of thefirst and second torque-limiting interfaces move over the other asopposed to with each other. When rotating a torque limiting assemblywithin a plastic body with an attachment at the circumferential rim theplastic body will tend to melt if sufficient frictional forces areapplied.

In FIG. 2, aspects and variations of assembly of a torque-limitingdevice are shown. The driver has a generally cylindrical shape with acup shaped drive cap 12 with connector mount or other structure tofacilitate use by a user. For example, the drive cap is affixed to agenerally hollow cylindrical body 14. The cap 12 is mated to thecylindrical body at the proximal end 15 of the cylindrical body. The cap12 may be snap-fitted to cylindrical body 14, or may be welded, adhered,or attached by any equivalent thereof.

The hollow cylindrical body 14 has an open distal end 16 with acircumferential rim 17 on the exterior therein proving a seat and guidefor a tool collar 20. A lower shank 100 is fit inside the body 14.Opposite the circumferential rim on the interior 18 of the cylindricalbody 14 is an upper shank component 200 formed as part of thecylindrical hollow body 14 with at least an axial bore 210 and atorque-limiting interface 250 disposed on the inside of the cylindricalbody 14.

The tool collar is a guide for a shaft. The tool collar has a flange 22extending radially of a size and shape to fit rotatably into thecircumferential rim 17. The tool collar has a roughly square leg 25extending on one side of the flange 22 and a nose 27 extending on theopposite of the flange. A shaped channel 29 passes through the toolcollar thereby forming a fluid connection.

During assembly the lower shank component 100 fits movably within thehollow body 14. The lower shank has a drive shaft 110 therethrough. Onone side of the lower shank lower torque-limiting interface 150 and theother side of the lower shank 100 is a retaining cavity 103 whichprovides a volume to hold the MBWA 70 configured to position biasingelements, such as a MBWA 70. A tool shaft 32 fits firmly into the toolcollar channel 29. The tool shaft may be partially hollow. One or morecatches 33 are formed on a portion of the tool shaft whereby the catchesmate with the channel 29 and the tool shaft 32 is restricted fromrotation within the channel 29. The catches are depicted as one or moreflat sides in FIGS. 1A-1C. A tool channel 34 extends axially, at leastpartially, in the tool shaft. A series of threads 35 are formed on aportion of the tool shaft 32. A first washer 36C, a second washer 36D,and a flat roller bearing washer ′36 is interposed between the flangeand circumferential rim 17.

The lower shank 100 is once inserted into the body 14 through theproximal end 15 and the lower torque-limiting interface 150 sits on theupper torque-limiting interface 250. The square leg and tool shaftextends through the axial bore 210 and the drive shaft 110. Formed aspart of the drive shaft 110 are a series of drive catches 115 which matewith the square legs 25 whereby when the lower shank 100 rotates thesquare leg rotates as does any tools 40 affixed therein.

The threaded 37 retaining member 38 such as a nut or other fixture fitsonto the threads 35 of the tool shaft and is used to compress the MBWA70 against the lower shank and hold the components inside the deviceinline. This engagement provides a locking mechanism for tool shaft 32relative to the body 14 via lower shank 100 when pressure is appliedacross lower shank 100 and upper shank 200. A preselected force isapplied across lower shank 100 and upper shank 200 via MBWA 70 withincylindrical body 14. To seal the device, the drive cap is mountedthereon. At the end of the drive cap 12 is formed a handle 44 for manualuse. The MBWA in the manual device preferably provides a force ofbetween about 5 N-m and about 13 N-m.

FIGS. 3, 4, and 5 show some additional details and aspects of someimplementations of torque-limiting mechanisms of the present disclosure.The torque-limiting mechanisms have the upper shank component 200, thelower shank component 100, and a biasing coil spring configured to applya force (F) along an axis 50. Upper shank component 200 can have aproximal end 201, a distal end 202, an axial bore 210 connecting theproximal end and the distal end, and a torque-limiting interface 250disposed on the proximal end. Lower shank component 100 can have aproximal end 101, a distal end 102, a drive socket 110 connecting theproximal end and the distal end, and a torque-limiting interface 150disposed on the proximal end. The upper shank component and the lowershank component are aligned along an axis 50 in the direction of theaxial bore 210 and the drive socket 110 with the torque-limitinginterface 250 in contact with the torque-limiting interface 150. Thebiasing element is configured to apply a compressive force (F) along theaxis to compress the torque-limiting interface against thetorque-limiting interface. The upper shank component 200 and the lowershank component 100 are configured to engage to generally nest with eachother and rotate together when torque is applied to the lower shankcomponent via the drive socket and are configured to disengage when apredetermined torque limit is exceeded. When disengaged, thetorque-limiting interfaces 150/250 slide past each other in relativerotation about the axis 50. Drive socket 110 can have any suitable shapethat allows for the transmission of torque to the lower shank component100. Suitable shapes for the drive socket 110 include geometric shapeprofiles such as hexagons, squares, or truncated/rounded versionsthereof.

Those of ordinary skill in the art can appreciate that thetorque-limiting mechanisms of the present disclosure can be incorporatedinto any systems or devices that require torque-limited rotation betweensubcomponents of those systems or devices. In some implementations, thetorque-limiting mechanisms of the present disclosure can be incorporatedinto torque-limited drivers for use in surgical applications; suchdrivers can be hand-driven or driven with power tools at higher rates ofrotation.

FIGS. 4A-4G and 5 show further aspects of some implementations. Uppershank component 200 can have a torque-limiting interface 250 with aplurality of undulations 220 arranged around the axial bore andseparated by a plurality of transition regions 224. The lower shankcomponent 100 can have a torque-limiting interface 150 having aplurality of undulations 120 arranged around the drive socket andseparated by a plurality of transition regions 124, the first and secondpluralities being equal in number. Each undulation 120/220 can be formedas an upslope 121/221, a peak 122/222, and a downslope 123/223.

The undulations 220 are not gears and are complex shaped waves tobalance maintaining nominal torque over a specific number of actuationsand limit degradation of inexpensive plastic materials which form theundulations. Such materials will degrade, overheat and/or melt and failmore quickly if subjected to unnecessary friction caused by contact atthe torque-limiting interface 150. By shaping specific portions of anundulation 220 as shown in sections A-A through E-E (see FIGS. 6B-6F)the balance of sufficient performance at nominal torque versusdegradation is accomplished. Section A-A (FIG. 6C) has a higher shouldernear the center (axial bore 210) of the shank and a slope downward 402to the perimeter of the shank. Contact between the upper and lowershanks at this section is minimized. This contact area is not themaximum torque transfer area. Section B-B is a region of greatercompressive force and by spreading the higher load across a widerplateau 404 the stress on the plastic shanks is distributed in thishigher compressive force region. Section C-C provides the widest plateau406 to further distribute the compressive forces which increase as thelower shank 100 moves around the upper shank 200 along the direction ofarrow 1000. Section D-D is the maximum height “H” plateau 408 of theundulation and it is where the maximum compressive forces are appliedbetween shanks, it is a wide plateau to distribute the load. Section E-Eprovides a transition region wherein compressive forces are reduced andthe area of is reduced via a sloping region 410. Shaped undulationsdisclosed herein maintain predetermined torque ranges without addingexcessive wear and heat to the assembly.

In some implementations, the torque-limiting interfaces 150/250 do notcontain any step or drop-off greater than about 0.005″. One or morecutouts or slots (not shown) can be provided in one or more of theupslopes, 121/221, peaks 122/222, or downslopes 123/223 to collect atleast a portion of any debris generated during operation. In someembodiments, downslope 123/223 is designed with maximum length toprovide the softest downward angle back down to the initial height ofthe next upslope 121/221. During powered rotation, a softer downslopemitigates degradation of the downslope 123/223 material. Suchdegradation adversely impact performance as the torque-limit at whichdisengagement occurs can change as the material degrades.

Each undulation 120/220 sweeps through a portion of the 360 degreesaround the central axial bore 210 or drive socket 11, with the pluralityof undulations 120/220 covering a total portion of the 360 degreesaround the central axial bore. In some implementations, the totalportion covered by the plurality of undulations 120/220 can be at leastabout 65% of the 360 degrees (about 235 degrees), at least about 70% ofthe 360 degrees (about 255 degrees), at least about 80% of the 360degrees (about 285 degrees), at least about 83% of the 360 degrees(about 300 degrees), at least about 90% of the 360 degrees (about 324degrees), at least about 95% of the 360 degrees (about 345 degrees), orat least about 98% of the 360 degrees (about 350 degrees). The portionnot covered by the plurality of undulations 120/220 is filled withtransition regions 124/224 between the end of each downslope 123/223 andthe beginning of the next upslope 121/221. Each transition region124/224 can be selected to be no greater than about 35 degrees, nogreater than about 20 degrees, no greater than about 15 degrees, nogreater than about 10 degrees, no greater than about 5 degrees, nogreater than about 4 degrees, no greater than about 3 degrees, nogreater than about 2 degrees, no greater than about 1 degree, or can beeliminated entirely if the end of each downslope 123/223 is immediatelyadjacent to the beginning of the next upslope 121/221.

A softer downslope angle the torque-limiting interfaces 150/250 cansubstantially mitigate or eliminate any “click” or audible indicationthat the upper shank component 200 and lower shank component 100 haveslipped past each other during a disengagement, also referred to hereinas an actuation, when the predetermined torque limit has been exceeded.In some implementations, an actuation indicating system can beincorporated in the overall torque-limiting driver to create one or more“clicks” when the upper shank component 200 and lower shank component100 have slipped past each other. In some implementations, the actuationindicating system can include a flag feature on either lower shankcomponent 100 or upper shank component 200 that impacts one or morespokes, protrusions, or other physical features on another component inthe system as relative rotation occurs.

Upper shank component 200 and lower shank component 100 can be formedfrom various materials. Suitable materials include stainless steels,aluminums, plastic materials, or composites including plastic. Plasticand other economical equivalents improve cost efficiency of productionwhile providing high tensile strength, resistance to deformation, etc.Effective materials include plastics, resins, polymers, imides,fluoropolymers, thermoplastic polymers, thermosetting plastics, and thelike as well as blends or mixtures thereof. In some implementations, 30%glass-filled polyetherimide can be used to form one or more of the abovecomponents. For components formed from stainless steels or aluminums,the shank components can be heat treated, passivated, or anodized viasuitable methods known to those of ordinary skill in the art. In someimplementations, aluminum shank components can be finished with a hardanodize finish per MIL-A-8625F, type III, class 2. In someimplementations, stainless steel 440c shank components can be heattreated per AMS 2759/5D to 58Rc and passivated with treatment withnitric acid and/or sodium dichromate. Other heat treatments andpassivation methods known in the art are also suitable. In someimplementations, corresponding pairs of gear rings are formed fromdifferent materials. In some preferred implementations, one shankcomponent 100/200 is formed from stainless steel or aluminum and thecorresponding gear ring is formed from 30% glass-filled polyetherimide(PEI) resin. In some implementations the shank components 100/200 can bemade from the same material.

According to aspects of one or more exemplary implementations,components of the torque-limiting mechanisms of the present disclosureare resistant to sterilization, cleaning, and preparation operations.For example, the upper shank component and lower shank component may beconfigured to withstand sterilization by methods including radiation(e.g., gamma rays, electron beam processing), steam (e.g., autoclave),detergents, chemical (e.g., Ethylene Oxide), heat, pressure, inter alia.For example, materials may be selected according to resistance to one ormore selected sterilization techniques.

The material selection and surface treatments applied to thetorque-limiting interfaces 150/250 can affect the predetermined torquelimit. The static friction between the torque-limiting interfaces150/250 determines when disengagement will occur, as the rotation forcecan overcome the static friction holding the interfaces into engagementwith each other. Greater contact surface area of the opposinginterfaces, via wider undulations 120/220 or other aspects of theshape/profile of the undulations 120/220, will increase the resistanceto actuation and lead to a higher predetermined torque limit.

In some preferred implementations, upper shank component 200 and lowershank component 200 are both mad from 30% glass-filled polyetherimide(PEI) resin. In some implementations, a glass-filled ULTEM® PEI fromSaudi Basic Industries Corporation (SABIC) can be used to form the uppershank component 200 and lower shank component 200 via machining ormolding. In some implementations, a lubricant is disposed on one or bothof torque-limiting interfaces 150/250. Such lubricants are useful toavoid excessive heat build-up during actuations at high rates ofrotation, which can melt or degrade the PEI material.

The shape of some implementations of undulations 120/220 can be seen inFIGS. 6A-6F. FIG. 6A shows a top view of the torque-limiting interface150 at the proximal end 201 of upper shank component 200. FIG. 6B showsa cut-away view of the upper shank component 200 along line A-A shown inFIG. 6A. FIG. 6C shows a cut-away view of the upper shank component 200along line B-B shown in FIG. 6A. FIG. 6D shows a cut-away view of theupper shank component 200 along line C-C shown in FIG. 6A. FIG. 6E showsa cut-away view of the upper shank component 200 along line E-E shown inFIG. 6A. FIG. 6F shows a cut-away view of the upper shank component 200along line D-D shown in FIG. 6A. The number of undulations 120/220 isdetermined by the size of the upper shank component 200 and lower shankcomponent 100 and the shape of the undulations 120/220. The size of theshank components 100/200 determines the functional path length that theplurality of undulations may have. The functional path length refers tothe circumferential length of a circular path along the midpoint of theundulations, shown as a dashed circle 227 in FIG. 6A. A larger diametershank component allows for a larger functional path length. The shape ofthe undulations 120/220 refers to the inclination angle of the upslope121/221, the length of the peak 122/222, and the declination angle ofthe downslope 123/223. Sharper inclination and declination angles andshorter peak lengths can lead to a shorter functional path length foreach individual undulation, which would allow for more undulations to beplaced onto the torque-limiting interfaces 150/250. The torque-limitinginterfaces may have two undulations, three undulations, fourundulations, or five or more undulations. Three or more undulations areused in some preferred implementations, as systems with only twoundulations may be less stable during actuations at higher rates ofrotation.

The width of the undulations can span the entirety of the annular ringof the proximal ends of the upper shank component and lower shankcomponent between the drive socket 110 or axial bore 210 and outer edgesof those components, or can be reduced widths to accommodate adjoiningparts to avoid undesired contact points or friction. The width must besufficient to provide adequate interface contact area with the opposingset of waves to create the friction necessary for torque transmission.Larger widths allow for the applied force to be distributed over largersurface areas and reduce stress on the components.

The inclination angle of each upslope 121/221 can be about 3 to about 15degrees, more preferably about 5 to about 9 degrees, more preferablyabout 6 to about 8 degrees, and most preferably about 7 degrees. Theinclination angle is measured along the functional path length along themidpoint of the undulations, as the angle along the interior edge126/226 will be higher due to the shorter path length, and the anglealong the exterior edge 125/225 will be lower due to the longer pathlength. The declination angle of each downslope 123/223 can be about 5to about 45 degrees, more preferably about 10 to about 30 degrees, morepreferably about 10 to about 20 degrees, and most preferably about 15degrees. The declination angle is measured along the functional pathlength along the midpoint of the undulations. In some preferredimplementations, the ratio of the functional path length of the upslope121/221 of each undulation to the functional path length of thedownslope of each undulation can be about 3.0:1, about 2.5:1, about2.4:1, about 2.3:1, about 2.2:1, about 2.1:1, about 2.0:1, about 1.9:1,about 1.8:1, about 1.7:1, about 1.6:1, about 1.5:1, about 1.4:1, about1.3:1, about 1.2:1, about 1.1:1, or about 1.0:1. In some preferredimplementations the ratio can be between about 2.2:1 and about 1.8:1, ormore preferably about 2.0:1.

Each peak 122/222 has an even height across its surface from theinterior edge 126/226 to the exterior edge 125/225 at each radial linefrom the central axis of the respective shank component 100/200. In someimplementations the functional path length of each peak 122/222 isapproximately equal to the length of each of the transition regions124/224, such that the peaks 122/222 of each torque-limiting interfaceare complementary and mate with the transition regions 124/224 of theopposing torque-limiting interface.

FIGS. 7A-7D show some aspects of an implementation of a lower shankcomponent 100 the present disclosure. FIG. 7A and FIG. 7B showperspective views of an implementation of a lower shank component 100.FIG. 7C shows a side view while FIG. 7D shows a cross-sectional viewalong the line D-D shown in FIG. 7C. The lower shank component 100 caninclude a retaining cavity 103 configured to retain biasing elementwithin an annular wall 104 located at the distal end 102. The retainingcavity 103 provides for a volume in which a biasing element 300 can becompressed, so that if biasing element 300 expands radially duringcompression it will be retained within retaining cavity 103 rather thanimpinging or contacting other components within the system.

Biasing element 300 provides compressive force between the upper shankcomponent and lower shank component to place the torque-limitinginterfaces 150/250 into frictional contact with each other. Suitablebiasing elements can include springs, spring washers, also referred toas Belleville washers, grommets or washers of compressible materialssuch as rubber. In some implementations, compressible materials withdurometer ratings between about 50 durometer and 100 durometer can beused as biasing elements. The biasing element can be compressed by othercomponents in a torque-limiting driver. The amount of compressionapplied to a biasing element can be used to set the predetermined torquelimit at which disengagement/actuation of the torque-limiting mechanismoccurs. Higher compressive forces created by the biasing element willcreate higher predetermined torque limits.

According to aspects of one or more exemplary implementations, thetorque-limiting mechanisms of the present disclosure are capable ofimparting torques of up to about 6 N-m at various rotational speeds. Forexample, the torque output range may be selected between about 0.5 N-mand about 6 N-m and utilized in combination with a rotational speedselected between about 150 RPMs and about 1300 RPMs. Typically, thetorque requirement is different for different operations and fordifferent implants. For example, applications may include those in thefield of orthopedic surgery, construction and emplacement of implants,etc. In such instances, the predetermined torque limit may be about 6N-m, depending on an implant's specifications. Smaller fasteners mayutilize lower torque limits between about 0.1 N-m and about 2.0 N-m. Insome instances the torque-limiting mechanisms of the present disclosurewill provide a predetermined torque of at least one of 0.1, 0.2, 0.3,0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7,1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1,3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5,4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, or6.0 Newton-meters (N-m) of torque at a rotational speed of at least oneof 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700,750, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1250, or 1300RPMs over at least one of 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100,105, 110, 120, 150, 180, 200, 220, 250, 300, 350, 400, 450, 500, 550,600, 650, 700, 750, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200,1250, 1300, 1350, 1400, 1450, 1500, 1550, 1600, 1650, 1700, 1750, 1800,1850, 1900, 1950, or 2000 actuations while remaining within a specifiedoperational range.

FIGS. 6A and 6B show testing data of an implantation of atorque-limiting mechanism of the present disclosure. A torque-limitingdriver that incorporated a torque-limiting mechanism having thetorque-limiting interfaces shown in FIGS. 2, 3, and 6A-6F formed from30% glass-filled PEI resin was assembled and tested at 450 RPM with apredetermined torque limit of about 1.05 N-m. The torque-limiting driverwas rotated at 450 RPM for 1 second intervals and the torque output wasmeasured with an electronic torque transducer. FIG. 8A shows that thetorque limit remained within an operational range of about 0.9 to about1.1 N-m over approximately 2,200 actuations. FIG. 8B shows data for two1-second intervals and shows the actuations that occur over those1-second intervals. Approximately 22 actuations, from 7.5 revolutionsper second at 450 RPM, occur in each 1-second interval, with the appliedtorque remaining within the operational range.

FIGS. 8C and 8D show the torque output profiles of torque-limitingdrivers over a single hand-driven actuation. FIG. 8C shows the torqueprofile of a traditional crown gear interface with opposing sets ofjagged teeth, such as that disclosed in U.S. Pat. No. 7,938,046,incorporated herein in its entirety for all purposes. The resultingprofile shows a spike drop-off in torque as the opposing teeth slip offeach other sharply. Systems incorporating these jagged teeth crown gearsexhibit inconsistent torque-limits across ranges of rotational speeds,with higher rotational speeds showing higher torque. In contrast, FIG.6D shows a torque output profile from the system used in FIGS. 6A and6B, which incorporates the three-undulation torque-limiting interfacesshown in FIGS. 2, 3, 4A-4F and described more fully elsewhere herein.The torque output increases and decreases more gradually and smoothlythrough each actuation, which provides for a more consistenttorque-limit across rotational speeds, including higher rotationalspeeds up to 1300 RPM. Further, the torque-limiting mechanisms are moredurable and can last through a higher number of actuations, includingover 2,000 actuations, while remaining within a specified operationalrange.

While the method and agent have been described in terms of what arepresently considered to be the most practical and preferredimplementations, it is to be understood that the disclosure need not belimited to the disclosed implementations. It is intended to covervarious modifications and similar arrangements included within thespirit and scope of the claims, the scope of which should be accordedthe broadest interpretation so as to encompass all such modificationsand similar structures. The present disclosure includes any and allimplementations of the following claims.

It should also be understood that a variety of changes may be madewithout departing from the essence of the disclosure. Such changes arealso implicitly included in the description. They still fall within thescope of this disclosure. It should be understood that this disclosureis intended to yield a patent covering numerous aspects of thedisclosure both independently and as an overall system and in bothmethod and apparatus modes.

Further, each of the various elements of the disclosure and claims mayalso be achieved in a variety of manners. This disclosure should beunderstood to encompass each such variation, be it a variation of animplementation of any apparatus implementation, a method or processimplementation, or even merely a variation of any element of these.

Particularly, it should be understood that as the disclosure relates toelements of the disclosure, the words for each element may be expressedby equivalent apparatus terms or method terms—even if only the functionor result is the same.

Such equivalent, broader, or even more generic terms should beconsidered to be encompassed in the description of each element oraction. Such terms can be substituted where desired to make explicit theimplicitly broad coverage to which this disclosure is entitled.

It should be understood that all actions may be expressed as a means fortaking that action or as an element which causes that action.

Similarly, each physical element disclosed should be understood toencompass a disclosure of the action which that physical elementfacilitates.

Any patents, publications, or other references mentioned in thisapplication for patent are hereby incorporated by reference. Inaddition, as to each term used it should be understood that unless itsutilization in this application is inconsistent with suchinterpretation, common dictionary definitions should be understood asincorporated for each term and all definitions, alternative terms, andsynonyms such as contained in at least one of a standard technicaldictionary recognized by artisans and the Random House Webster'sUnabridged Dictionary, latest edition are hereby incorporated byreference.

In this regard it should be understood that for practical reasons and soas to avoid adding potentially hundreds of claims, the applicant haspresented claims with initial dependencies only.

Support should be understood to exist to the degree required under newmatter laws—including but not limited to United States Patent Law 35 USC132 or other such laws—to permit the addition of any of the variousdependencies or other elements presented under one independent claim orconcept as dependencies or elements under any other independent claim orconcept.

To the extent that insubstantial substitutes are made, to the extentthat the applicant did not in fact draft any claim so as to literallyencompass any particular implementation, and to the extent otherwiseapplicable, the applicant should not be understood to have in any wayintended to or actually relinquished such coverage as the applicantsimply may not have been able to anticipate all eventualities; oneskilled in the art, should not be reasonably expected to have drafted aclaim that would have literally encompassed such alternativeimplementations.

Further, the use of the transitional phrase “comprising” is used tomaintain the “open-end” claims herein, according to traditional claiminterpretation. Thus, unless the context requires otherwise, it shouldbe understood that the term “compromise” or variations such as“comprises” or “comprising”, are intended to imply the inclusion of astated element or step or group of elements or steps but not theexclusion of any other element or step or group of elements or steps.

Such terms should be interpreted in their most expansive forms so as toafford the applicant the broadest coverage legally permissible.

1. A disposable torque limiting device comprising: a generally hollowcylindrical body (14) with a partially closed distal end (16); an uppershank (200) formed inside the partially closed distal end of thecylindrical body; a circumferential rim (17) formed on the inside of thepartially closed dial end; an upper torque-limiting interface (250)formed on the inside of the partially closed distal end having a axialbore (210); a lower shank component (100) comprising a proximal end(101), a distal end (102), a drive shaft (11) extending from the distalend a drive socket (110) fluidly connecting the proximal end and thedistal end, and a lower torque-limiting interface (150) disposed on theproximal end; wherein the lower shank component is rotatable with in thecylindrical body and the upper shank component and the lower shankcomponent are aligned along an axis (50) in the direction of the axialbore, the lower shank component is rotatable with in the cylindricalbody and the drive socket with the first torque-limiting interface incontact with the second torque-limiting interface; a biasing element 300is placed above the lower shank on at least partially around a toolshaft (32) configured to apply compressive force (F) along the axis tocompress the first torque-limiting interface against the secondtorque-limiting interface; a tool collar (20) with a flange (22)extending radially, a front (23) on one side of the flange, a square leg(25) formed on the opposite of the flange and a shaped channel (29)there through rotatably fit into the circumferential rim; the tool shaft(32) has a threaded back portion (35) and a front end (31) having a toolchannel (34) therein; catches (33) formed on the tool shaft configuredto mate with the shaped channel whereby the tool shaft can be insertedthrough the tool collar and restrict rotation within the shaped channel;a threaded (37) retaining member (38) configure to engage the threadedback portion; wherein the tool shaft and threaded retaining membercooperate to apply a predetermined force to the lower and upper shanksvia affixation of the tool shaft through the tool collar, the axialbore, the drive socket and the MBWA and affixing the retaining memberthereto.
 2. The device of claim 1 wherein: the biasing element appliescompressive force (F) along the axis to compress the firsttorque-limiting interface against the second torque-limiting interface;the upper shank component and the lower shank component are configuredto engage to rotate together when torque is applied to the lower shankcomponent via the drive socket; and, the upper shank component and thelower shank component are configured to disengage when a predeterminedtorque limit is exceeded.
 3. The device of claim 1 further comprising aplastic high lubricity washer between the flange and the circumferentialrim.
 4. The device of claim 1 further comprising a roller bearing washer(36′) between the flange and the circumferential rim.
 5. The device ofclaim 1 further comprising a tool (40) in the tool channel.
 6. Thedevice of claim 1 wherein the first torque-limiting interface and secondtorque-limiting interface each comprise three undulations (220).
 7. Thedevice of claim 6 wherein each undulation is a complex shaped wave whichlimits degradation of inexpensive plastic materials and provides nominaltorque.
 8. The device of claim 6 further comprising: a first section ofeach undulation with a higher peak (222) near the interior edge (226) ofthe shank and a downslope (223) to the perimeter of the upper shank(200); and, a second section having a wide upslope (221).
 9. A torquelimiting drive comprising: an upper shank (200) formed inside thepartially closed distal end of the cylindrical body; a circumferentialrim (17) formed on the inside of the partially closed dial end; an uppertorque-limiting interface (250) having undulations formed on the insideof the partially closed distal end having an axial bore (210); a lowershank component (100) rotatable placed within the cylindrical bodycomprising a proximal end (101), a distal end (102), a retaining cavity(103) formed therein, a drive socket (110) fluidly connecting theproximal end and the distal end, and a lower torque-limiting interface(150) having undulations disposed on the proximal end, wherein the uppershank component and the lower shank component are aligned along an axis(50) in the direction of the axial bore and the drive socket with thefirst torque-limiting interface in contact with the secondtorque-limiting interface; a biasing member (300) within the retainingcavity configured to apply compressive force (F) along the axis tocompress the first torque-limiting interface against the secondtorque-limiting interface at a predetermined torque limit; a tool collar(20) with a flange (22) extending radially, a front (23) on one side ofthe flange, a square leg (25) formed on the opposite of the flange and ashaped channel (29) there through rotatably fit into the circumferentialrim; a tool shaft (32) with a threaded back portion (35) and a front end(31) having a tool channel (34) therein; and, a threaded (37) retainingmember (38) configure to engage the threaded back portion.
 10. Thedevice of claim 9 wherein each undulation is a complex shaped wave whichlimits degradation of inexpensive plastic materials and provides nominaltorque.
 11. The device of claim 10 further comprising: a first sectionof each undulation with a higher peak (222) near interior edge (226) ofthe shank and a downslope (223) to the perimeter of the upper shank(200); and, a second section having a wide upslope (221).
 12. The deviceof claim 11 wherein: the biasing member is configured to applycompressive force (F) along the axis to compress the firsttorque-limiting interface against the second torque-limiting interface;the upper shank component and the lower shank component are configuredto engage to rotate together when torque is applied to the lower shankcomponent via the drive socket; and, the upper shank component and thelower shank component are configured to disengage when a predeterminedtorque limit is exceeded.
 13. The device of claim 9 further comprising aroller bearing washer (36′) between the flange and the circumferentialrim.
 14. The torque-limiting device of claim 9 wherein: the undulationsof the first torque-limiting interface are arranged around the axialbore and separated by a first plurality of transition regions (224); theundulations of the second torque-limiting interface are arranged aroundthe drive socket and separated by a second plurality of transitionregions (124), the first and second pluralities being equal in number;and each undulation comprises an upslope (121/221), a peak (122/222),and a downslope (123/223).
 15. The torque-limiting device of claim 14wherein each upslope has an inclination angle between about 3 degreesand about 15 degrees.
 16. The torque-limiting device of claim 14 whereineach upslope has an inclination angle between about 5 degrees and about9 degrees.
 17. The torque-limiting device of claim 14 wherein thepredetermined torque limit is between about 0.1 Newton-meters and 3.0Newton-meters.
 18. The torque-limiting device of claim 14 wherein thepredetermined torque limit is between about 3.0 Newton-meters and 6.0Newton-meters.
 19. The torque-limiting device of claim 14 wherein thefirst torque-limiting interface and second torque-limiting interfaceeach comprise between two and five undulations.
 20. The torque-limitingdevice of claim 11 further comprising a power unit attached to the driveshaft.
 21. The torque-limiting device of claim 11 wherein thetorque-limiting mechanism provides a predetermined torque between about0.1 Newton-meters and about 6 Newton-meters of torque at a rotationalspeed between about 50 RPM and about 1300 RPM over at least one of 5,10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 105, 110, 120, 150, 180, 200,220, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850,900, 950, 1000, 1050, 1100, 1150, 1200, 1250, 1300, 1350, 1400, 1450,1500, 1550, 1600, 1650, 1700, 1750, 1800, 1850, 1900, 1950, 2000, 2100,2200, 2300, 2400, or 2500 actuations while remaining within a specifiedoperational range.